The present invention relates to integrated circuits (ICs), and more particular to a method of fabricating an IC which includes at least a low-dielectric constant, k, interlevel dielectric film having improved adhesion, low-defect density and enhanced electrical properties associated therewith.
The semiconductor industries drive to continually improve density and performance has forced the use of advanced interconnect structures. For example, copper, Cu, has been introduced as a wiring technology for 0.22 xcexcm generation and below products, and by the 0.13 xcexcm generation, it is expected that low-k dielectrics (materials that have a relative dielectric constant of 3.8 or below) will be combined with copper interconnects to further improve performance.
In the case of metallization, the choice of the new wiring material is reasonably straight forward, but the choice of the intermetal dielectric (IMD) is not as clear. Many new low-k dielectrics which are based on spin-on organic or glass materials have become recently available to the semiconductor industry. Extensive characterization and integration efforts are however needed to select appropriate candidates and then incorporate these materials into semiconductor products.
During the material selection process for IMD, emphasis is often placed on the electrical and chemical properties of the material. For example, an IMD for advanced interconnect applications must exhibit a low-dielectric constant, low-leakage, high-breakdown strength and good thermal stability at typical processing temperatures.
Although there maybe great emphasis on these properties during the initial evaluation process, mechanical properties and manufacturability issues play a large role, perhaps even a dominant role, in the selection of a dielectric for use in semiconductor manufacturing. For example, mechanical properties such as chemical-mechanical polishing (CMP) and packaging operations may damage soft dielectric structures; therefore the mechanical properties and manufacturability must also be taken into careful consideration when selecting an IMD.
Moreover, for many low-dielectric constant materials, an adhesion promoter is typically needed to ensure efficient adhesion of the low-k dielectric to the substrate. This in itself is a concern since many of the presently available low-k dielectrics such as spin-on organic or glass materials are extremely sensitive to defects caused by particle contamination which, in turn, may cause the dielectric to breakdown under bias at low-electrical fields. As such, typical adhesion promoters known in the art cannot be employed for low-k dielectrics.
U.S. Pat. Nos. 4,950,583 and 4,732,858 to Brewer, et al. describe an adhesion promoting product and process for treating an integrated substrate. Specifically, Brewer, et al. describe the use of alkoxysilane to improve the adhesion of a photoresist to a substrate as well as adding an activating catalyst to the alkoxysilane to enhance bonding at the interface. Further, Brewer, et al. describe the addition of an adjuvant polymer, such as methyl cellulose, to the alkoxysilane to enhance bonding to interfaces. In some examples, heating of the adhesion promoter (110-140xc2x0 C. for 15-30 minutes) to improve adhesion is recommended.
The current invention describes a process to adhere an IMD to a substrate or interconnect layer to produce excellent adhesion after repeated thermal cycles while maintaining the electrical properties of the IMD (i.e., defect free films). The process entails spin applying the adhesion promoter, baking to promote reaction, rinsing with a solvent to remove the unreacted adhesion promoter (to prevent the formation of particulate defects in the subsequent IMD layer) followed by coating of the IMD layer. The process described by Brewer, et al. would result in a high concentration of particulate defects in the IMD rendering it unreliability and ineffective as an insulator.
U.S. Pat. No. 5,760,480 to You, et al. describe the use of a silane-based adhesion promoter which can be applied between the metal and dielectric layer or which can be incorporated in the dielectric layer. The current invention, as mentioned above, describes a process to adhere an IMD to a substrate or interconnect layer to produce excellent adhesion after repeated thermal cycles while maintaining the electrical properties of the IMD (i.e., defect free films). You, et al. do not describe a process or procedure to effectively utilize an adhesion promoter with a spin-on dielectric insulator.
In view of the drawbacks mentioned hereinabove concerning low-k dielectrics, there is a need for developing a method in which a low-k dielectric can be used in back-end of the line (BEOL) processing in which the low-k dielectric has improved adhesion, low-defect density and good electrical properties.
The present invention is directed to a method of fabricating an IC which includes at least a low-k dielectric material in contact with a substrate, wherein the low-k dielectric exhibits improved adhesion to the substrate and is substantially-free of defects. Such an IC can be obtained in the present invention by utilizing processing steps which include application of a high-concentration of a silane-coupling agent to a substrate, as well as a heating step and a rinsing step. It has been unexpectedly determined that each of these processing steps, which will be defined in more detail below, are essential in providing an IC which includes a substantially defect-free, low-k dielectric that has improved adhesion properties as well as good electrical properties.
Specifically, the processing steps of the present invention comprise:
(a) applying a silane-coupling agent containing at least one polymerizable group to a surface of a substrate so as to provide a substantially uniform coating of said silane-coupling agent on said substrate;
(b) heating said substrate containing said coating of said silane-coupling agent at a temperature of about 90xc2x0 C. or above so as to provide a surface layer on said substrate containing Sixe2x80x94O bonds;
(c) rinsing said heated substrate with a suitable solvent that is effective in removing any residual unreacted silane-coupling agent; and
(d) applying a dielectric material to said rinsed surface containing said Sixe2x80x94O bonds.
The silane-coupling agent employed in the present invention serves as an adhesion promoter for the dielectric material without causing any significant formation of defects therein. Moreover, by employing the silane-coupling agent of the present invention, it is possible to apply a low-k dielectric having a relative dielectric constant of about 3.8 or below in step (d) above. This allows for the formation of an interconnect structure having a substantially defect-free, low-k dielectric as an interlayer or intralayer dielectric.